---
id: cython-lint
version: "0.21.0"
license: unclear
license_treatment: permissive
maintenance: active
---

# cython-lint — Lint Cython files

License: permissive · Maintenance: active · Downloads: 859.6K/mo

## What it is and what it does

cython-lint is a static analysis tool that checks Cython (.pyx) files for code quality issues, unused imports, undefined variables, style violations, and Cython-specific problems. It combines pycodestyle checks with custom rules for patterns that are particularly error-prone in Cython code—such as dangerous default values, late-binding closures, and repeated dict keys—and can be run from the command line or integrated into pre-commit workflows.

The tool is designed to catch issues that flake8 historically missed in Cython files. It supports configuration via command-line arguments or a `.cython-lint.toml` / `pyproject.toml` file, allows selective rule ignoring, and includes an automated fixer for quote normalization. Its runtime dependencies are minimal and well-established (cython, pycodestyle, tokenize-rt, tomli), making it straightforward to integrate into existing Python development environments.

Use it for:

- Enforce code quality standards in Cython-heavy projects like NumPy, pandas, or scikit-learn before commits.
- Catch unused imports and variables in Cython modules during CI/CD pipelines via pre-commit hooks.
- Identify Cython-specific anti-patterns (late-binding closures, dangerous defaults) that pure Python linters miss.
- Normalize quote style in Cython files across a project using the double-quote-cython-strings fixer.
- Configure project-wide linting rules in pyproject.toml to maintain consistent Cython code style.

## Worth the install?

AI-flagged interpretation of the facts above — verify before relying.

A linter for Cython files that checks for common errors, style issues, and code quality problems using pycodestyle rules and Cython-specific checks, with support for pre-commit hooks and automated fixes.

Yes. cython-lint is actively maintained, has low install friction, carries no security vulnerabilities, and is widely adopted by major scientific Python projects. If you work with Cython code, it fills a real gap that general Python linters leave open. The permissive MIT license removes any legal concern. Install it if you want to catch Cython-specific bugs and style issues early.

## Install

pip install cython-lint
uv add cython-lint
poetry add cython-lint

## Installing cython-lint

Before you install: Low friction install with four straightforward runtime dependencies (cython, pycodestyle, tokenize-rt, tomli). Actively maintained with recent releases; last commit was 2026-08-10 and the project is not archived.

License in practice: Licensed under MIT (permissive), so you can use, modify, and distribute this package freely in both open-source and commercial projects without significant legal restrictions.

Quickstart:

pip install cython-lint

# Command-line usage
cython-lint my_file.pyx

# Or configure in .pre-commit-config.yaml:
# - repo: https://github.com/MarcoGorelli/cython-lint
#   rev: v0.21.0
#   hooks:
#   - id: cython-lint

Requires Python 3.10 or later.

Verify before relying:

- Whether the tool's Cython-specific checks cover all common pitfalls in production codebases, or if gaps remain.
- Performance characteristics when linting large Cython projects with many files.
- How well the automated fixer (double-quote-cython-strings) integrates with other formatters like black.

## Package facts

- License: not declared (permissive)
- Python support: supports_current
- Install friction: low
- Maintenance: active
- Downloads: 859.6K/month (top 5,000 on PyPI)
- Known vulnerabilities: none known

## Tags

cython linter, lint cython files, cython code quality, cython pre-commit hook, cython style checker, cython error detection, cython pyx linter, cython, linting, pre-commit

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